Medically reviewed by
Diana Morgan, MS, CISSN
7 min read
Vitamin C and D are essential vitamins that help support your health, but is it possible to have too much of a good thing? Short answer: Yes. You can take too much of both vitamins. However excessive, prolonged intake of vitamins C and D is not common. That said, like any other supplement, vitamins C and D intake should not exceed the tolerable upper intake level (UL) and you should follow the suggested use for taking them safely. Overall, make sure you check with your healthcare practitioner if you have any questions about taking any supplement.
Vitamin C is a water-soluble vitamin and powerful antioxidant. Most commonly you might think of vitamin C when you think of citrus fruits like oranges but you can find vitamin C in a large number of foods you consume daily. Think peppers, strawberries, tomatoes, and even broccoli. Vitamin C helps play a critical role in immune health. making sure you're getting enough vitamin C — either from your diet or by supplementing — can help support healthy immune function.
Vitamin C is most commonly known for its ability to support the immune system and its immune health benefits have long been studied by researchers and scientists. While evidence is mixed, most of this research on vitamin C points to positive benefits on the immune system. One meta-analysis reviewed 60+ studies on the effect of vitamin C on the common cold and concluded that while vitamin C does not help prevent colds in normal adults, it may help support healthy immune function.
Vitamin C (ascorbic acid) is considered a potent antioxidant involved in sequestering free radicals to minimize the damage they cause to our bodies due to oxidative stress. Vitamin C is also well known as a “helper vitamin” for Iron. Research has shown that taking vitamin C can help our bodies better absorb iron from food or supplements.
Fun fact: In the 1700s, scurvy was a common problem for sailors on long trips out at sea and in 1747, a Scottish Naval surgeon, James Lind, discovered citrus fruits, high in vitamin C, can help prevent scurvy.
Unlike vitamin C, vitamin D is a fat-soluble vitamin. This means that your body absorbs vitamin D the same way you would absorb fats in your diet. While you can get vitamin D from foods in your diet like sardines, egg yolks, and cheese) most people get their daily dose from sunlight. Exposure to the sun, specifically UV rays, helps your body naturally synthesize vitamin D from cholesterol stores in your skin. A number of factors impact the ability for people to get necessary levels of Vitamin D through sun exposure. Regional factors that prevent people from getting sun exposure include wearing sunblock, cloud cover patterns, smog, and the angle at which the sun hits the earth where you live. In this case supplementation may be a good option for you.
Vitamin D is available in two forms: D2 (ergocalciferol) and D3 (cholecalciferol).
Vitamin D influences many systems and processes within our bodies, particularly bone health and immune health. A few well known benefits of vitamin D include:
Researchers have also concluded that increased vitamin D supplementation during pregnancy may reduce negative consequences associated with inflammation. And a panel of experts concluded “that a cause and effect relationship has been established between the dietary intake of vitamin D and contribution to the normal function of the immune system and healthy inflammatory response, and maintenance of normal muscle function.”
Yes, while rare, it is possible to overdose on vitamin C and vitamin D. Significantly large doses of either vitamin are required to trigger an overdose. The risk of an overdose, however minor, should still be taken seriously and we recommend consulting with your physician to determine the vitamin C and D doses that are best for you.
The recommended daily amount of vitamin C is 65 mg to 90 mg daily, but as always, check with your doctor to determine the right amount for your needs. It is essential to find a high quality vitamin C supplement if you plan on taking a daily vitamin to get the most benefits from your vitamin C. Look for a supplement that resembles Vitamin C in its food-based form and is designed for easier absorption.
The FDA recommends between 400 and 800 IUs per day for children and adults. If you aren’t getting this amount from your diet or the sun, supplementing with a high quality supplement is a good place to start. The best way to know if you’re getting enough vitamin D is to take a blood test. A doctor can give you the 25(OH)D test. When choosing your vitamin D supplements, look for Vitamin D3, the most common and bioavailable form of vitamin D.